1. Field of the Art
The present invention relates to a positioning system and, more particularly, to a positioning system wherein a transport car that levitatively travels along a transport path out of contact with the transport path is stopped at a predetermined stop position by a magnetic attraction force while levitating above the transport path.
2. Prior Art
FIG. 13 shows one example of a conventional positioning system for stopping a transport car at a predetermined stop position. A transport car 1 which travels in a direction X has magnetic members 2 provided on the bottom surface thereof, as shown in FIGS. 15(A) and 15(B), which illustrate the structure of the transport car 1 in detail. It should be noted that wheels 23 are not needed during ordinary travel in a magnetic levitation transport system wherein the transport car 1 is levitatively suspended and not in contact with a can-shaped partition 20 by levitation magnetic poles (not shown) provided outside the partition 20 and provided with propelling force by a linear motor (not shown) which is also provided outside the partition 20 so that the transport car 1 levitatively travels inside the can-shaped partition 20.
Transport car 1 has secured to the bottom surface thereof magnetic member 2 in the form of an iron core and being a secondary-side magnetic member. On the other hand, a primary-side electromagnet 4 is disposed at a stop position on a transport path 3 in such a manner that pole-face 4a of the electromagnet 4 faces the secondary-side magnetic member 2. By energizing a coil 5 wound on the primary-side electromagnet 4 when the transport car 1 reaches stop position, the pole-face 2a of the secondary-side iron core 2 is attracted to the pole-face 4a of the electromagnet 4, thereby enabling the transport car 1 to be stopped at a predetermined position in a non-contact manner.
FIG. 14 illustrates the relationship between the displacement X of the transport car 1 from the stop position (equilibrium position) and restoring force f during the above-described stopping operation. As will be understood from the FIG. 14, when the displacement X is positive, a negative restoring force f acts, whereas, when the displacement X is negative, a positive restoring force f acts. Accordingly, the transport car 1 having inertial force vibrates about the point of displacement x=0 (equilibrium point), and such vibration is damped by the action of air resistance, resistance by eddy current loss, and so forth. Eventually, the transport car 1 stops at the equilibrium point.
Since this type of non-contact positioning system stops the transport car by applying a braking force thereto in a non-contact manner, it has advantages in that there is no wear of a contact surface, no dust is generated, and hence maintenance is facilitated in comparison to other positioning systems that utilize a mechanical frictional force. Accordingly, if such a non-contact type positioning system can be incorporated into a magnetic levitation transport system or the like, in which a transport car is levitatively suspended and driven horizontally by a linear motor, it is possible to realize a transport system in which levitative support, driving and braking of the transport car can be all effected in a non-contact manner. Thus, such a transport system is extremely suitable for use in a clean area in which generation of dust must be avoided.
However, when the above-described non-contact type positioning system is incorporated into a magnetic levitation transport system or the like, the following problems arise: If a transport car, which is levitatively supported in the vertical direction by a magnetic attraction force and driven horizontally by a linear motor for traveling and which thus has inertial force, is stopped by the positioning system in which a restoring force acts, as shown in FIG. 14, the transport car vibrates in the travel direction or other direction about the equilibrium point (x=0), as described above. In this case, since the transport car is in a non-contact state, no frictional resistance occurs, but only a damping force acts thereon by the action of air resistance, eddy current loss, and so forth. For this reason, the vibration cannot readily be damped, and it takes a great deal of time to stop the transport car.
In view of the above-described problems of the prior art, an object of the present invention is to provide a positioning system which may be incorporated into a magnetic levitation or other non-contact type transport system and which is capable of stopping a transport car in a short period of time.